1. Field of the Invention
This invention relates to an apparatus for stretching a highly elastic material such as bread dough, and particularly to an apparatus for stretching bread dough that is continuously supplied by a conveyor, so as to form a thin and continuous sheet of bread dough, by simply applying vibrations, thereby easily forming a high-quality sheet of bread dough with a constant thickness and uniform inner layers.
2. Prior Art
To stretch elastic materials, a stress higher than their yield point has customarily been applied to them. However, the elasticity thus lost has not been automatically recovered. Therefore, in producing food, especially bread that requires elasticity as an important quality, a skilled manual operation has always been necessitated.
When bread is automatically produced by machinery, maintaining the elasticity of the bread dough is always considered troublesome. Moreover, if even a little of the elasticity is lost, it is difficult to produce bread having a taste like that in bread made by a skilled artisan. Therefore, potassium bromate and the like have been mixed in the material as chemical additives, and the stretched bread dough has then been put in a rest condition so that the elasticity (membrane-forming function) lost due to the machinery could be recovered.
Thus, the conventional method of stretching bread dough caused its inherent elasticity to be partly lost. Further, the twisting stress caused by any screw mechanism has been imparted to the bread dough, and has broken the gluten's gel structure so as to also cause the elasticity to be partly lost. To recover it, the chemical additives were added to the bread dough. However, as compared with the taste of manually-prepared bread, an inferior taste was obtained. In any event, using the chemical additives was an unnatural resolution of the problem.
Therefore, the applicant disclosed in U.S. Pat. No. 5,804,225 an invention entitled "A Stretching Method and Apparatus" wherein highly viscous and elastic dough can be stretched into a thin sheet of dough (Japanese Patent Application 7-317211). It discloses an apparatus for stretching dough by planetary rollers that revolve along a circular orbit while rotating about their own axes. Below the rollers a conveying device is provided to provide a curved gap between the rollers and the device, the gap being gradually narrowed from the inlet to the outlet for the dough. The conveying device comprises a plurality of rollers and is adapted such that the peripheral speed of the rollers is gradually increased from the inlet to the outlet for the dough.
It was found that this apparatus can sufficiently stretch bread dough even when it has a high viscosity and high elasticity. However, the conveying device comprises only a plurality of rollers. Namely, due to a space between adjacent rollers, no continuous and generally flat conveying surface is provided. Therefore, a part of the bread dough tends to hang between the adjacent rollers. Thus, a sufficient stretching of the bread dough cannot be attained. This leads to a wrinkled sheet of bread dough. In other words, the poor stretching by this apparatus causes the dough to wrinkle, and thus a sufficiently uniform and sufficiently thick sheet of bread dough is not obtained.